A supercharged or turbocharged engine may include a compressor recirculation valve for relieving pressure downstream of a compressor during conditions where it may not be desirable to provide greater pressure than atmospheric pressure upstream of a throttle. For example, if a driver is requesting a relatively high driver demand torque followed by a low driver demand torque, it may be desirable to reduce pressure upstream of an engine intake manifold throttle so that the engine may provide torque closer to the driver demand torque. The pressure downstream of a compressor may be relieved via opening a compressor recirculation valve in response to the low driver demand torque. However, air in an engine intake system may be mixed with fuel vapors and contaminants that may pass through the engine's air intake filter. The fuel vapors and contaminants may build up over time in the compressor recirculation valve causing a change in the compressor recirculation valve's flow characteristics. Therefore, the compressor recirculation valve may not provide an expected amount of airflow during some conditions.
The inventors herein have recognized the above-mentioned issues and have developed a diagnostic method, comprising: partially opening a waste gate and adjusting a compressor recirculation valve to a closed position in response to a diagnostic request; incrementally opening the compressor recirculation valve after the compressor recirculation valve is closed; adjusting a compressor recirculation valve airflow offset in response to waste gate position while incrementally opening the compressor recirculation valve from the closed position; and operating the compressor recirculation valve in response to the airflow offset.
By adjusting a compressor recirculation valve airflow offset in response to a waste gate position, it may be possible to provide the technical result of improving engine air intake pressure control even when deposits are formed within a compressor recirculation valve. In one example, the recirculation valve airflow offset may be determined based on a change in position of the waste gate when the waste gate is closed loop controlled to maintain a desired pressure at an inlet of an engine intake manifold throttle. Specifically, the recirculation valve may be first closed and then incrementally opened. The recirculation valve opening position where the waste gate position is changed to maintain constant engine intake manifold throttle inlet pressure may be determined to be the compressor recirculation valve offset value. The waste gate position may be adjusted in response to pressure at the inlet of the engine intake manifold throttle to maintain engine airflow and reduce the possibility of disturbing a driver.
The present description may provide several advantages. For example, the approach may improve engine airflow at low driver demand levels. Further, the approach may improve engine air-fuel ratio control during accelerator pedal tip-out conditions. Further, the approach may be applied to turbocharged or supercharged engines.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.